BOMP methodology

The ecology of the Barn Owl—an elusive, predominantly nocturnal species which is found at low densities, does not sing and calls relatively infrequently—means that the species is most easily surveyed by monitoring their potential nest sites each year. Visiting nest sites during the breeding season also provides an opportunity to record nesting attempts and collect information on productivity.

For BOMP, participants could register any number of potential Barn Owl nesting sites (usually boxes) they intended to monitor. They would then visit their registered sites throughout the breeding season and collect the following information:

1. Site Details

Information about the type of nest site registered, such as the box design and siting. Different types of nest site may influence the success of birds breeding at the site.
The location of the registered site (i.e. six-figure grid reference, held in the strictest confidence). Breeding success may vary geographically due to a range of factors including weather conditions and road densities.
Information on the habitat types around the registered site and other important features present (ditches, railway embankments etc). Breeding success is likely to be influenced by food availability. Different habitats around the nest site may support different numbers of favoured prey species.

2. Site occcupancy

Whether a registered site is occupied by Barn Owls. Site occupancy provides a minimum estimate of the number of Barn Owls in an area. If occupancy declines substantially between years, then this may provide an early warning that abundance might be changing.

BOMP participants were asked to record occupancy for each of their registered sites, even if it meant sending in a 'nill return' (i.e. no boxes occupied). Participants were also asked to record the presence of other species inhabiting potential Barn Owl nest sites, such as Kestrel, Tawny Owl, Little Owl, Jackdaw and Stock Dove.

3. Nest Contents

BOMP used Nest Record Scheme methodology to record counts of eggs and young and the outcome of active nests. These observations allowed the calculation of productivity measures such as average clutch size, average brood size and nest failure rate. Ideally, nests were visited on two or more occasions and the contents recorded on standard BTO nest record cards or using the home computer inputting program IPMR (Integrated Population Monitoring Reporter).

Barn Owl Schedule 1 status

It is important to remember that Barn Owls are listed on Schedule 1 of the Wildlife & Countryside Act 1981 and a Schedule 1 Licence must therefore be obtained before approaching any nest site. For more information about obtaining such a licence, please contact the jez.blackburn [at] bto.org (subject: Barn%20Owl%20Schedule%201%20enquiry) (Licensing Officer) at the BTO.

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